1. Field of the Invention
Systems, apparatuses, and methods consistent with the present invention relate to protecting data, and more particularly, to protecting against unauthorized copying of audio/video (AV) contents by using copy control information (CCI) included in an AV stream.
2. Description of the Related Art
Generally, an AV stream includes content and copy control information indicating the status of a copy control of the content. That is, the copy control information indicates whether an AV stream processing system, for example, a recorder implemented by hardware or software, has an authorization to copy the content included in the AV stream received from a transmitting medium. The recorder, for example, decrypts the content based on a value of the copy control information.
The copy control information may be indicated with bits, as predetermined within the AV stream, for example, with a 2-bit code. Four types of modes capable of constituting the copy control information are listed in Table 1 as follows.
TABLE 1Operation modes of an AV apparatus according to CCI informationCCI code and status of AV streamDescription of operation00‘copy free’Contents are not encrypted, copyingthereof is unrestricted01‘copy free but encrypted’Contents are encrypted but copyingthereof is unrestricted10‘copy one generation’Contents are encrypted, and only onecopying thereof is allowed. After theone copying, CCI information ischanged to ‘no more copy’11‘no more copy or copyContents are encrypted, and nonever’copying thereof is allowed
FIG. 1 illustrates a schematic structure of an AV stream 100. The AV stream 100 comprises a content field which includes contents and an information field which includes information on the contents. The information field comprises a region 110 for copy control information, which is used to control a copying operation of an AV apparatus, and information on a variety of contents contained in the AV stream 100. The content field is divided into n sub-unit regions, that is, ‘Content_unit_1,’ ‘Content_unit_2,’ . . . ‘Content_unit_n.’
The region 110 included in the information field for copy control information (“first copy control information”) is divided into regions corresponding to the number of the sub-units. Each of the divided regions comprises a copy control information value, such as 00, 01, 10 and 11, and location information of a corresponding one of the sub-units. The location information may comprise physical or logical addresses for the corresponding sub-unit, or time information relating to when the content in the sub-unit is played. FIG. 1 refers to the location information as ‘unit_1_ptr,’ ‘unit_2_ptr,’ . . . ‘unitn_ptr.’
A sub-unit may be divided into one or more regions. By way of example, a sub-unit included in the content field, that is, ‘Content_unit_2’ may be divided into three small regions of ‘Sub_2_1,’ ‘Sub_2_2’ and ‘Sub_2_3,’ and each of the small regions may include a corresponding copy control information 130 thereto.
The copy control information included in each sub-unit of the content field (“second copy control information”) is used to generate a decryption key to decrypt the content, and thus, if it is modified, the contents cannot be decrypted. For example, the copy control information 130 of Sub_2_1 is used to generate a decryption key to decrypt the content of Sub_2_1. However, the first copy control information 110 is used to control a copying operation, and thus, an unauthorized copying of the contents becomes possible as a third party may change the first copy control information 110.
FIG. 2 shows a conventional AV stream data copy protection system to protect contents from being copied without authorization from an owner of the contents. The AV stream data copy protection system 200, which decrypts encrypted AV stream data, comprises an AV stream receiving unit 210, a control unit 220, a decryption key generating unit 230, and a content interpreting unit 240. The AV stream receiving unit 210 receives AV stream data. The control unit 220 receives a control signal to control an operation of an AV apparatus, input from the outside. The control signal may comprise a command signal to play the content or a command signal to copy the content. Referring to FIG. 1, the control unit 220 receives the first copy control information 110 transmitted from the AV stream receiving unit 210, and transmits a control signal corresponding to a value of the first copy control information 110 to the decryption generating unit 230 and the content interpreting unit 240.
In detail, the AV stream receiving unit 210 receives AV stream data, and transmits to the control unit 220 the first copy control information 110 included in the AV stream data. The control unit 220 receives a control signal to control an operation of an AV apparatus from the outside. When the control signal is a command signal to copy content, the control unit 220 checks an encryption status of AV contents in the AV stream data received by the AV stream receiving unit 210, by referring to the first copy control information 110.
When a value of the first copy control information 110 is ‘copy free,’ there is no need to generate a decryption key, and thus, the control unit 220 allows the content interpreting unit 240 to transmit the AV stream data to an output device 250 as received by the AV stream receiving unit 210. When the value of the first copy control information 110 is ‘no more copy or copy never,’ ‘copy free but encrypted,’ or ‘copy one generation,’ data is required to be decrypted. Accordingly, the decryption key generating unit 230 receives the first copy control information 110 from the control unit 220, generates a decryption key by using the second copy control information 130 and other information from the AV stream receiving unit 210, and transmits the decryption key to the content interpreting unit 240. The content interpreting unit 240 decrypts a content field of the AV stream data received by the AV stream receiving unit 210, by using the decryption key, and transmits decrypted AV content to an output device 250, such as a storage medium or a displaying apparatus.
The conventional AV stream data copy protection system 200 uses the first copy control information 110 to check whether an AV apparatus has an authorization to copy the contents. However, the first copy control information 110 may be easily modified to facilitate unauthorized copying of the contents. Therefore, for example, when ‘no more copy or copy never’ (11) or ‘copy one generation’ (10) is modified to ‘copy free but encrypted’ (01), or when ‘no more copy or copy never’ (11) is modified to ‘copy one generation’ (10), and such modified information is received by the AV stream receiving unit 210 of the conventional AV stream data copy protection system 200, the control unit 220 may falsely confirm that copying of an AV stream has been allowed. Accordingly, unauthorized copying of the contents may be accomplished.